commit - 562cace75e1d775536106561ec459bbdd51e5388
commit + d2f25f66d712a2d3cfdfa79a23a4df06dc2d8922
blob - f6b4392c49275c136533ae25814b6a3b9c861784
blob + e82dbf124ff526f0b4a7da01956dff6ff19c852d
--- src/day-6.lisp
+++ src/day-6.lisp
@@ -3,40 +3,36 @@
   (:export #:day-6))
 (in-package #:aoc/day-6)
 
-(defun task-1 (times distances)
-  (loop with task-1 = nil
-        for time in times
-        for distance in distances
-        do (push (loop for speed from 1 below time
-                       for remaining-time = (- time speed)
-                       for travelled = (* speed remaining-time)
-                       when (> travelled distance)
-                         sum 1 fixnum)
-                 task-1)
-        finally (return (apply #'* task-1))))
+(declaim (ftype (function (fixnum fixnum fixnum) t) beats-distance-p)
+         (inline beats-distance-p))
+(defun beats-distance-p (speed time distance)
+  (let* ((remaining-time (- time speed))
+         (travelled (the fixnum (* speed remaining-time))))
+    (> travelled distance)))
 
-(defun join-numbers (numbers)
-  (parse-integer (apply 'concatenate 'string
-                        (mapcar #'write-to-string numbers))))
-
-(defun task-2 (time distance)
+(declaim (ftype (function (fixnum fixnum) fixnum) possible-ways-to-beat))
+(defun possible-ways-to-beat (time distance)
   (let ((start (loop for speed from 1 below time
-                     for remaining-time = (- time speed)
-                     for travelled = (* speed remaining-time)
-                     when (> travelled distance)
+                     when (beats-distance-p speed time distance)
                        do (return speed)))
         (end (loop for speed from (1- time) downto 1
-                   for remaining-time = (- time speed)
-                   for travelled = (* speed remaining-time)
-                   when (> travelled distance)
+                   when (beats-distance-p speed time distance)
                      do (return speed))))
     (- end start -1)))
 
+(defun join-numbers (numbers)
+  (parse-integer (apply 'concatenate 'string
+                        (mapcar #'write-to-string numbers))))
+
 (defun day-6 (input)
   (let* ((line (read-line input))
          (times (read-number-list line :start (1+ (position #\: line))))
          (line (read-line input))
          (distances (read-number-list line :start (1+ (position #\: line)))))
-    (values (task-1 times distances)
-            (task-2 (join-numbers times)
-                    (join-numbers distances)))))
+    (values (loop with task-1 fixnum = 1
+                  for time in times
+                  for distance in distances
+                  do (setf task-1 (* task-1 (possible-ways-to-beat time distance)))
+                  finally (return task-1))
+            (possible-ways-to-beat (join-numbers times)
+                                   (join-numbers distances)))))